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Until the sender sends the image of whatever it should have been without copying / pasting, then you will never know.
Ask the sender to insert the image from a file on their system rather than using copy paste and then you will see the image they are trying to send you.

This is usually down to the person who sent the message copying / pasting an image into an email rather than inserting an image. When an image is pasted, rather than inserted, it results in the red cross that you see.

Not much you can do apart from inform the sender and ask them to insert the image.

That is usually solved by deleting everything under the C:\Documents and Settings\username\Local Settings\Temporary Internet Files.
It happens more often than not with roaming profiles but not necessarily.
That folder is supposed to get cleared on logoff but sometimes it doesn't happen and things get corrupted there. That's when users will start getting a red x instead of images.

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